System and method for mitigating against ionospheric gradient threats for aerial platforms

Abstract

A method includes repeatedly determining a distance of an aircraft from a landing location. The method also includes, during a first stage in which the aircraft is at least a threshold distance from the landing location, performing iono-free processing during navigation of the aircraft. The method further includes, during a second stage in which the aircraft is less than the threshold distance from the landing location and a velocity of the aircraft is greater than a velocity threshold, performing divergence-free processing during navigation of the aircraft to address possible ionospheric threats. In addition, the method includes, during a third stage in which the aircraft is less than the threshold distance from the landing location and the velocity of the aircraft is less than the velocity threshold, calculating one or more floor values for a Differential Ionospheric Correction (DIC) sigma, and determining a navigation solution to protect against nominal ionospheric conditions.

What is claimed is: 
     
       1. A method comprising:
 repeatedly determining a distance of an aircraft from a landing location; 
 during a first stage in which the aircraft is at least a threshold distance from the landing location, performing iono-free processing during navigation of the aircraft; 
 during a second stage in which the aircraft is less than the threshold distance from the landing location and a velocity of the aircraft is greater than a velocity threshold, performing divergence-free processing during navigation of the aircraft to address possible ionospheric threats; and 
 during a third stage in which the aircraft is less than the threshold distance from the landing location and the velocity of the aircraft is less than the velocity threshold, calculating one or more floor values for a Differential Ionospheric Correction (DIC) sigma, and using the one or more floor values to determine a navigation solution that protects against threats due to nominal ionospheric conditions. 
 
     
     
       2. The method of  claim 1 , further comprising:
 during the third stage, performing Ionospheric Gradient H1 (IGH1) calculations to determine a set of protection levels that protect the navigation solution against threats from non-nominal ionospheric conditions. 
 
     
     
       3. The method of  claim 1 , wherein the velocity threshold comprises a minimum aircraft velocity to observe a spatial ionospheric gradient. 
     
     
       4. The method of  claim 1 , wherein performing the iono-free processing comprises:
 calculating iono-free pseudo-range observables and iono-free carrier phase observables using raw pseudo-range and carrier phase measurements from one or more reference Global Navigation Satellite System (GNSS) receivers. 
 
     
     
       5. The method of  claim 1 , wherein performing the divergence-free processing comprises:
 selecting a buffer sample rate and a buffer size based on the velocity of the aircraft and a minimum distance over which a spatial ionospheric gradient is observable, wherein the buffer sample rate and the buffer size are associated with a data buffer for one or more system reference and aircraft ionosphere measurements. 
 
     
     
       6. The method of  claim 5 , wherein the buffer sample rate and the buffer size are selected to satisfy the following equation:
   Relative_aircraft_velocity*Buffer_Sample_Rate*Buffer_Size= D,    
 
       wherein Relative_aircraft_velocity is the velocity of the aircraft, Buffer_Sample_Rate is the selected buffer sample rate, Buffer_Size is the selected buffer size, and D is the minimum distance over which the spatial ionospheric gradient is observable. 
     
     
       7. The method of  claim 5 , wherein the buffer sample rate is selected to be a multiple of a data rate processing speed. 
     
     
       8. A device comprising:
 at least one processor configured to:
 repeatedly determine a distance of an aircraft from a landing location; 
 during a first stage in which the aircraft is at least a threshold distance from the landing location, perform iono-free processing during navigation of the aircraft; 
 during a second stage in which the aircraft is less than the threshold distance from the landing location and a velocity of the aircraft is greater than a velocity threshold, perform divergence-free processing during navigation of the aircraft to address possible ionospheric threats; and 
 during a third stage in which the aircraft is less than the threshold distance from the landing location and the velocity of the aircraft is less than the velocity threshold, calculate one or more floor values for a Differential Ionospheric Correction (DIC) sigma, and use the one or more floor values to determine a navigation solution that protects against threats due to nominal ionospheric conditions. 
 
 
     
     
       9. The device of  claim 8 , wherein the at least one processor is further configured to:
 during the third stage, perform Ionospheric Gradient H1 (IGH1) calculations to determine a set of protection levels that protect the navigation solution against threats from non-nominal ionospheric conditions. 
 
     
     
       10. The device of  claim 8 , wherein the velocity threshold comprises a minimum aircraft velocity to observe a spatial ionospheric gradient. 
     
     
       11. The device of  claim 8 , wherein, to perform the iono-free processing, the at least one processor is configured to:
 calculate iono-free pseudo-range observables and iono-free carrier phase observables using raw pseudo-range and carrier phase measurements from one or more reference Global Navigation Satellite System (GNSS) receivers. 
 
     
     
       12. The device of  claim 8 , wherein, to perform the divergence-free processing, the at least one processor is configured to:
 select a buffer sample rate and a buffer size based on the velocity of the aircraft and a minimum distance over which a spatial ionospheric gradient is observable, wherein the buffer sample rate and the buffer size are associated with a data buffer for one or more system reference and aircraft ionosphere measurements. 
 
     
     
       13. The device of  claim 12 , wherein the at least one processor is configured to select the buffer sample rate and the buffer size to satisfy the following equation:
   Relative_aircraft_velocity*Buffer_Sample_Rate*Buffer_Size= D,    
 
       wherein Relative_aircraft_velocity is the velocity of the aircraft, Buffer_Sample_Rate is the selected buffer sample rate, Buffer_Size is the selected buffer size, and D is the minimum distance over which the spatial ionospheric gradient is observable. 
     
     
       14. The device of  claim 12 , wherein the at least one processor is configured to select the buffer sample rate to be a multiple of a data rate processing speed. 
     
     
       15. A non-transitory computer readable medium containing instructions that when executed cause at least one processor to:
 repeatedly determine a distance of an aircraft from a landing location; 
 during a first stage in which the aircraft is at least a threshold distance from the landing location, perform iono-free processing during navigation of the aircraft; 
 during a second stage in which the aircraft is less than the threshold distance from the landing location and a velocity of the aircraft is greater than a velocity threshold, perform divergence-free processing during navigation of the aircraft to address possible ionospheric threats; and 
 during a third stage in which the aircraft is less than the threshold distance from the landing location and the velocity of the aircraft is less than the velocity threshold, calculate one or more floor values for a Differential Ionospheric Correction (DIC) sigma, and use the one or more floor values to determine a navigation solution that protects against threats due to nominal ionospheric conditions. 
 
     
     
       16. The non-transitory computer readable medium of  claim 15 , wherein the medium contains instructions that when executed cause the at least one processor to:
 during the third stage, perform Ionospheric Gradient H1 (IGH1) calculations to determine a set of protection levels that protect the navigation solution against threats from non-nominal ionospheric conditions. 
 
     
     
       17. The non-transitory computer readable medium of  claim 15 , wherein the velocity threshold comprises a minimum aircraft velocity to observe a spatial ionospheric gradient. 
     
     
       18. The non-transitory computer readable medium of  claim 15 , wherein the instructions that when executed cause the at least one processor to perform the iono-free processing comprise:
 instructions that when executed cause the at least one processor to calculate iono-free pseudo-range observables and iono-free carrier phase observables using raw pseudo-range and carrier phase measurements from one or more reference Global Navigation Satellite System (GNSS) receivers. 
 
     
     
       19. The non-transitory computer readable medium of  claim 15 , wherein the instructions that when executed cause the at least one processor to perform the divergence-free processing comprise:
 instructions that when executed cause the at least one processor to select a buffer sample rate and a buffer size based on the velocity of the aircraft and a minimum distance over which a spatial ionospheric gradient is observable, wherein the buffer sample rate and the buffer size are associated with a data buffer for one or more system reference and aircraft ionosphere measurements. 
 
     
     
       20. The non-transitory computer readable medium of  claim 19 , wherein the instructions when executed cause the at least one processor to select the buffer sample rate and the buffer size to satisfy the following equation:
   Relative_aircraft_velocity*Buffer_Sample_Rate*Buffer_Size= D,    
 
       wherein Relative_aircraft_velocity is the velocity of the aircraft, Buffer_Sample_Rate is the selected buffer sample rate, Buffer_Size is the selected buffer size, and D is the minimum distance over which the spatial ionospheric gradient is observable.